Typically in earth boring, a drill head on the top of a pipe which has interconnected rod sections is driven into the ground. A bentonite drilling fluid can be pumped to the drill head through the rod. The bentonite drilling fluid can issue through the drill head and can flush out drilling cuttings through an annular space formed around the rod. The bentonite drilling fluid can also be used to stabilize the drilling channel, to cool the drill head and can be used as a lubricant in addition to flushing out the drilling cuttings. The drill head can be flattened at the sides for direction control. When the drill head advances by rotating, it is possible to drill straight ahead. If the rotation of the drill head is suspended, the lateral flattening makes it possible to deviate from drilling straight ahead. In addition to a pushing drive, an optional hammer mechanism can be used, in particular to counteract poor conditions in the ground.
In earth boring, particularly when creating a pilot bore, a probe is introduced into the region of the drill head to locate the drill head and/or also to measure state variables such as temperature, pressure and the like. The signals from the probe can be transmitted wirelessly or by cable for location and/or in respect of the state variables. The probe can be powered by accumulators or batteries for transmission. Due to this type of power supply, the energy is restricted for wireless transmission, thereby resulting in a narrower transmission range and a short service life. To increase the transmission range, an external voltage source can be connected to operate the probe at a higher voltage. For this purpose, cables associated with the rod sections can be provided which can produce a conductive connection. The connection of the cables allows higher voltages, as a result of which the service life can also be prolonged.
For example, DE 10 2010 019 514 A1 discloses an auger device with a drill rod which has rod sections. Arranged inside a rod section is a segment of a conductor, the two ends of each segment having a contact element, via which an electrical connection of the two segments arranged in the rod sections is simultaneously achieved when two rod sections are screwed together, in that the front contact faces of the contact elements are pressed against each other. DE 10 2010 019 514 A1 states that while the segments of the electrical conductor are themselves insulated, an insulation of this type for the contact faces of the contact elements is not provided because these have to be interconnected in an electrically conductive manner. An electrical connection between a portion of the contact faces and for example the casing of the drill rod via the drilling fluid can result.
A disadvantage of this type of connection of the conductors guided in the rod sections is that it is necessary to control a voltage source such that, if there is an electrically conductive connection between the rod casing and the conductor due to the drilling fluid, the conductor does not function as an anode.